(1) Field of the Invention
This invention relates to an alloy for use in exhaust valves of various internal combustion engines.
(2) Description of the Prior Art
Heretofore, high-manganese austenite steel, SUH36 (Fe-8.5%Mn-21%Cr-4%Ni-0.5%C-0.4%N), has largely been used as an exhaust valve material for gasoline engines and diesel engines.
Lately, the trend to increasing the compression ratio and the output of engines has increased, and hence the service conditions of engine valves have become more severe.
According to the above, there are used Ni-based heat resistant alloys having excellent high-temperature strength and corrosion resistance such as NCF 751 (Ni-15.5%Cr-1%Nb-2.3%Ti-1.2%Al-7%Fe) and NCF 80A (Ni-19.5%Cr-2.5%Ti-1.4%Al).
However, these Ni-based heat resistant alloys contain a great amount of expensive nickel, so that the cost of a valve made therefrom is raised considerably.
Therefore, it is strong demand has arisen to develop valve materials durable under severe service conditions and cheap in cost. For this purpose, the inventors previously proposed Fe-Ni based heat resistant alloys (Japanese Patent Application No. 58-154504).